The present invention relates to a new and improved apparatus for the bellowless vulcanization of tire blanks, wherein the tire beads are pressed by a press mechanism against the foot or base region of the mold halves.
The use of an expandable and heatable bellows constitutes part of the state-of-the-art vulcanization devices which are generally employed in processes for vulcanization of tire blanks. The bellows serves to dish or arch the tire blank and to press the latter against the vulcanization mold.
The drawback of such technique resides, on the one hand, in the apparatus construction required for this purpose, and furthermore in the presence of the bellows itself which is subject to malfunction, and therefore at certain time-intervals must be exchanged. The necessary expenditure required for replacing the bellows and the therewith associated downtime of the vulcanization mold increases the costs for the production of the tires and maintenance of the equipment.
Furthermore, possible irregularities of the bellows are transferred to the finished vulcanized tire and this becomes perceptible during production. For instance, during the dishing operation weaker locations of the bellows tend to become markedly expanded, resulting in a pronounced elongation of the tire blank at the corresponding location. It is further to be mentioned that the bellows must be provided at its outer surface with a multiplicity of grooves in order to be able to withdraw the air between the tire blank and the bellows. During the vulcanization operation, these grooves are formed as ribs at the inside of the tire, with the result that deformations can occur at the inner carcass layers.
In order to counteract the aforementioned drawbacks, attemps have been made to conduct the vulcanization medium directly against the inner wall of the tire while dispensing with the use of the bellows. With this procedure, the tire beads of the tire blank are pressed by a press or pressure mechanism in the axial direction against the bead sections of the mold.
What is important in this regard is to attain a perfect seal at the region of a tire bead, since penetration of vulcanization medium between the outer wall of the tire and the mold causes reject of the tire.
The previously known techniques for the bellowless vulcanization possess the drawback that a certain region at the tire bead remains covered with respect to the vulcanization medium during the vulcanization process, which of course leads to a surge or jump in the temperature of the tire material at the correspnding location. However, the quality of the tire is dependent upon a uniform vulcanization of the entire tire.
With the previously known vulcanization apparatuses for carrying out a process of this type, the tire blank is pressed at the region of the tire bead against the bead section of the vulcanization mold by means of essentially disk-shaped press plates.
The shortcomings which arise with such type press plates are the following: firstly, it is difficult to configure such in a manner that it is possible to automatically change or load the vulcanization apparatus; additionally the tire blank becomes completely covered during the vulcanization process, so that temperature surges arise at the tire which considerably impair its quality.
There is further known to the art a vulcanization apparatus for carrying out a process of this type which possesses six rotatable rollers accommodated to the shape of the tire bead, the axes of rotation of which extend parallel to the tire radius. Consequently, there is present the drawback that owing to the few rollers which move at the periphery of the tire bead, the air cannot be completely pressed out of the vulcanization mold, and simultaneously during the roller movement there is present a brief raising or lift-off of the bead since the rollers tend to drive the raw rubber ahead of such in the manner of a wave, so that again air inclusions are formed which considerably impair the quality of the final product.